This proposal is designed to investigate the effects of polychlorinated biphenyls (PCB's), animal density and nutritional status alone and in combination on reproductive and related characteristics of two wild mammals, the pine vole, Microtus pinetorum and the cottontail rabbit, Sylvilagus floridanus. Animals will be housed in the laboratory and given different levels of PCB's in their feed after having been subjected to different nutritional levels (ad libitum or 30 percent restricted) and/or different cage densities (2 or 6 animals/cage). Barbiturate induced sleeping time will be determined as a reflection of hepatic xenobiotic metabolism before and after PCB treatment. Animals will then be killed and the following measurements taken to determine treatment effects: ovarian weight, follicle counts, pituitary weight, pituitary LH content, adrenal weight, adrenal and plasma corticoid levels.